Storage water heaters heat a volume of water in an insulated tank. Water is supplied to the tank from a cold water supply while water is drawn from the tank into a hot water pipe, which, for example, may lead to a faucet. Water in the tank is heated by an energy source. An example is an electrical heating element, and another is a flame, such as from a gas combustion source. A sensor controls the energy source.
Increases in the performance of storage water heaters over the years have been achieved by improvements in the tank, or in the efficiency of energy delivery into the volume of water. Insulation values have reached very high levels, and further improvements have been few.